serial: xuartps: Add some register initialisation to cdns_early_console_setup()

Add initialisation of control register and baud rate to
cdns_early_console_setup(), required when running kernel standalone
without a boot loader. Baud rate is only initialised when specified in
earlycon command-line option, otherwise it is assumed this has been
set by a boot loader. Updated Documentation/kernel-parameters.txt
accordingly.

Signed-off-by: Scott Telford <stelford@cadence.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 26 insertions, 1 deletions

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 39f41bfd7c22..f37edaa5ac75 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -1165,9 +1165,34 @@ static void __init cdns_early_write(struct console *con, const char *s,
 static int __init cdns_early_console_setup(struct earlycon_device *device,
                                            const char *opt)
 {
-        if (!device->port.membase)
+        struct uart_port *port = &device->port;
+
+        if (!port->membase)
                 return -ENODEV;
 
+        /* initialise control register */
+        writel(CDNS_UART_CR_TX_EN|CDNS_UART_CR_TXRST|CDNS_UART_CR_RXRST,
+               port->membase + CDNS_UART_CR);
+
+        /* only set baud if specified on command line - otherwise
+         * assume it has been initialized by a boot loader.
+         */
+        if (device->baud) {
+                u32 cd = 0, bdiv = 0;
+                u32 mr;
+                int div8;
+
+                cdns_uart_calc_baud_divs(port->uartclk, device->baud,
+                                         &bdiv, &cd, &div8);
+                mr = CDNS_UART_MR_PARITY_NONE;
+                if (div8)
+                        mr |= CDNS_UART_MR_CLKSEL;
+
+                writel(mr,   port->membase + CDNS_UART_MR);
+                writel(cd,   port->membase + CDNS_UART_BAUDGEN);
+                writel(bdiv, port->membase + CDNS_UART_BAUDDIV);
+        }
+
         device->con->write = cdns_early_write;
 
         return 0;